The present invention relates to a magnetic recording medium which can record a large volume of data and a method of manufacturing the same, and more particularly to a magnetic recording medium which is suitable for high density magnetic recording.
As can be understood from the recent tendency that not only personal computers but also home electric appliances incorporate compact large-capacity magnetic disk devices, demand for a larger capacity magnetic storage is growing and improvement in recording density is expected. In order to cope with this, efforts to develop new magnetic heads and magnetic recording media have been vigorously made. However, it is difficult to improve the recording density using the current commercial longitudinal magnetic recording system. Therefore, research has been made on perpendicular magnetic recording as an alternative to the longitudinal recording system. Perpendicular recording is considered to be essentially suitable for high density recording because neighboring magnetizations do not face each other and the condition of high density recording is stable. Also, a combination of a single pole type recording head and a double-layered perpendicular magnetic recording medium with a soft-magnetic underlayer can improve the writability and cope with an increase in coercivity of recording layer. However, it is necessary to achieve low media noise performance and high thermal stability in order to realize high density recording based on the perpendicular recording system.
For the recording layer of a perpendicular magnetic recording medium, research has been made on the use of CoCrPt alloy film which has been used for longitudinal magnetic recording media. In order to achieve low media noise performance using CoCrPt alloy film, Cr segregation to crystal grain boundaries must be used to reduce exchange coupling between magnetic crystal grains and make the magnetic reversal unit smaller. However, if the quantity of Cr is insufficient, low noise characteristic is not obtained since the insufficient Cr makes grains unite and become larger in the course of recording layer forming process or the decrease of exchange coupling among grains is insufficient. On the other hand, if the amount of Cr is large, much Cr remains in grains and the magnetic anisotropy energy of magnetic grains declines and satisfactory thermal stability cannot be attained.
In order to solve this problem and achieve low media noise performance, for example, as disclosed in JP-A No. 178413/2003, many studies have been made on a granular type recording layer of oxide-added CoCrPt alloy. When a granular type recording layer is employed, magnetic intergrain exchange coupling is reduced by forming an oxide grain boundary layer which surrounds magnetic grains and thus a CoCrPt alloy material with a high magnetic anisotropy energy may be used regardless of the Cr concentration. Also, since the oxide grain boundary layer is discontinuous with magnetic grains in terms of crystal and has some thickness, amalgamation of grains hardly occurs in the process of forming a recording layer. For this reason, a granular type perpendicular magnetic recording medium of oxide-added CoCrPt alloy is attracting attention as a candidate for a low-noise and thermally stable perpendicular magnetic recording medium. So far many researches have been made on the seed layer and intermediate layer of a perpendicular magnetic recording medium. For example, JP-A No. 162807/2003 discloses seed layers of B, C, Al, Si, P, Ti, Zr, Hf, Cr, V, Nb, Ta, Ru, Rd, Pd, Pt, Cu, Ag and Au, and NiAL and NiTa which combine these with a magnetic metal Fe, Co or Ni, and intermediate layers of Co, Cr, Pt, Pd, Rh and Ru alloy. In addition, it is reported, for example, in IEEE Transactions on Magnetics, Vol. 38, No. 5, p. 1976 (2002) that Ru is suitable for intermediate layers of oxide granular type perpendicular magnetic recording media. Also, it is reported, for example, in IEEE Transactions on Magnetics, Vol. 38, No. 5, p. 1979 (2002) that a Ta seed layer improves the crystal grain alignment of a Ru intermediate layer.